The present invention relates to a lamp, such as a vehicle headlight whose purpose is to light up the road or the route ahead of the vehicle. However, a lamp of the present invention can also be used in any type of lighting appliance, such as, for example, an overhead projector, a slide viewer, etc. The present invention is thus not limited to the particular use made of the lamp whose primary function is to illuminate or more precisely to direct a light beam in a given direction. In order to generate such a light beam, a light source must be placed in the lamp. The light source also generates heat and, in a motor vehicle headlight, that heat is considerable. It is therefore necessary to use materials adapted to withstanding such heat. This applies for all types of lamp serving to emit light. However, a preferred use remains use as a motor vehicle headlight. The present invention also relates to an overmolding tool for molding the lens support.
The particular type of lamp of the invention includes a lens support made of a plastics material and assembled to a reflector inside which a light source, e.g. a bulb, is placed. The lens support connected to the reflector also serves as support means for supporting an elliptical or aspherical lens which is preferably made of glass. Conventionally, such a lens has a substantially plane rear face facing towards the light source, i.e. towards the inside of the lamp, and an optical front face that is usually convex and that faces towards the outside of the lamp. However, the rear face can be convex or can have some other shape entirely. In addition, this type of lens is provided with a peripheral rim which connects its front face to its rear face. The peripheral rim serves in most cases as a member via which the lens can be held by the lens support. In other words, the lens support is fixed to the lens at the rim.
The present invention relates more particularly to the fixing mode whereby the glass lens is fixed to the lens support which is made of a plastics material. Numerous techniques already exist that are used to fix the lens to the lens support. The most well known fixing techniques use bonding with adhesive, snap-fastening, crimping, or other mechanical holding systems having deformable catches or pivotally mounted levers.
Those prior art fixing techniques suffer from drawbacks, in particular, the techniques using snap-fastening, crimping, or a mechanical holding system. A first drawback lies in the fact that, when the lens is made of glass, which it always is nowadays, said lens is relatively fragile and prone to breaking when it is subjected to an impact or to an excessive load. That applies precisely with the prior art fixing techniques in which it is difficult to control the forces or pressures generated by the snap-fastening, the crimping, or the mechanical holding means. As a result, in practice, the breakage rate for lenses during assembly is relatively large. A first object of the present invention is to remedy that drawback by reducing considerably, or even to zero, lens breakage rate while the lens is being assembled to the lens support.
Another problem related to fixing the lens to the lens support lies in the fact that the thickness of the rim on the lens can vary with tolerance conventionally being 3/10ths of a millimeter (mm). Given that it is the optical front face that must be positioned with precision relative to the light source because of its technical characteristics, it is very advantageous to use the front face and/or the front portion of the rim surrounding the front face as a reference for positioning the lens relative to the lens support. No fixing system in which the lens is placed on the lens via its rear face can guarantee that the front face is positioned properly relative to the light source. That can result in degraded optical characteristics for the lamp as a whole. Therefore, another object of the present invention is to guarantee that the optical front face of the lens is positioned with optical precision relative to the lens support.